In recent years, a solid-state image pickup apparatus is approximately classified into a type of CCD (charge coupled device) and a type of amplified solid-state image pickup apparatus in which each pixel has a signal amplification function. More specifically, in various amplified solid-state image pickup apparatuses, a CMOS (complementary metal-oxide semiconductor) sensor has been rapidly in practical use because a technique of reducing noises of the CMOS sensor was developed and the CMOS sensor excellently matches with a CMOS process. As a result, the CMOS sensors and the CCDs come to substantially divide the whole of the various solid-state image pickup apparatuses in two.
However, since the number of transistors which constitute the pixels of the CMOS sensor is extremely large, numerous wirings for controlling these transistors are necessary, whereby a multi-layer wiring must be adopted. For this reason, in the reduced-size pixel, the height of the opening of the wiring from the surface of a photodiode is high, and further the area of the opening is narrow. As a result, there is a problem that sensitivity of the CMOS sensor degrades.
In order to solve the above-described problem of the CMOS sensor, there are several proposals which concern the constitution of the pixel. One of these proposals is disclosed in the patent document 1 (Japanese Patent Application Laid-Open No. H09-046596). More specifically, the patent document 1 discloses that plural photodiodes share transistors constituting a pixel so as to reduce the number of transistor elements for each pixel. Besides, another proposal is disclosed in the patent document 2 (Japanese Patent Application Laid-Open No. H11-112018). More specifically, the patent document 2 discloses that the use of transistors for selection is eliminated.
Further, another proposal is disclosed in the patent document 3 (Japanese Patent Application Laid-Open No. H11-097662). More specifically, FIGS. 2 and 4 of the patent document 3 respectively disclose pixel wirings. That is, in the patent document 3, a power supply wiring for an amplification transistor and a pixel output wiring are constituted as vertical lines extending in a column direction. Further, driving wirings to be connected to the gates of pixel transistors such as a transfer transistor, a reset transistor and the like are constituted as horizontal lines extending in a row direction. By constituting a pixel as above, an opening can be made wider as much as possible.
Under the circumstances, in order to further reduce the number of wirings in the pixel of the CMOS sensor, it is conceivable that the pixels of two lines share a single power supply line so that one power supply wiring is provided for the two pixels lines. In this connection, the patent document 4 (Japanese Patent Application Laid-Open No. 2003-230055) discloses in FIG. 15 and the corresponding description that pixels of two lines are set to be symmetrical in regard to the boundary thereof, and that a power supply line is provided on the relevant boundary. According to such a pixel constitution of a CMOS sensor, since the area of an opening of a wiring can be widened, sensitivity of the CMOS sensor can be improved.
However, it should be noted that the following problem concerning image quality occurs in the constitution disclosed in the patent document 4. More specifically, FIG. 6 illustrates a wiring layout in 2×2 pixels according to the constitution disclosed in the patent document 4. In FIG. 6, numeral 16 denotes one pixel frame, and the four pixel frames 16 are arranged in the form of 2×2. Besides, a power supply wiring 6, a left-line pixel output wiring 7-1, and a right-line pixel output wiring 7-2 are arranged.
As can be seen from FIG. 6, in the symmetrical two pixel lines, it is believed that the left-line pixel output wiring 7-1, the right-line pixel output wiring 7-2 and the power supply wiring 6 are arranged on the pixel boundary in the vertical direction of the two pixel lines. For this reason, since the center of the wiring opening is shifted to closer one of the right and left ends of the two pixel lines, sensitivity of the right-line pixels in regard to oblique incident light is different from sensitivity of the left-line pixels in regard to oblique incident light.
In other words, the left-line pixels tend to have higher sensitivity in regard to right oblique incident light as compared with left oblique incident light, while the right-line pixels tend to have higher sensitivity in regard to left oblique incident light as compared with right oblique incident light. The solid-state image pickup apparatus receives light sent from a condensing lens. Here, in the solid-state image pickup apparatus, with respect to the pixel receiving the light transmitting through the center line of the lens, the left oblique incident light and the right oblique incident light have the same weight. However, with respect to the pixel apart from the center line of the lens, for example, the pixel apart from the center line of the lens in the left direction, an amount of the oblique incident light from the right is larger as compared with an amount of the oblique incident light from the left. Consequently, at that position, the sensitivity of the left-line pixel is high but the sensitivity of the right-line pixel is low. For this reason, even if uniform incident light is irradiated onto such a portion, pixel outputs vary at one-line intervals. Here, it should be noted that the pixels positioned apart from the center line of the lens in the right direction show a tendency opposite to that of the pixels positioned in the left direction. Consequently, even if uniform incident light is irradiated onto the pixel area, a difference between the output of the left-line pixel and the output of the right-line pixel becomes large according to the pixels positioned closer to the end of the pixel area in the horizontal direction. As a result, image quality deteriorates.
One reason of such a problem is that the numbers of the wirings to be arranged on the boundaries of the pixel lines are “0”, “3”, “0”, “3”, . . . in due order. Further, even if the pixel output wirings are arranged respectively at the left and right ends of the pixels of two pixel lines, the numbers of the wirings at the boundaries of the pixel lines are “2”, “1”, “2”, “1”, . . . . Thus, the wirings having the certain same number cannot be acquired at the boundaries of the respective lines, whereby the above problem cannot be solved. In addition, another reason of the above problem is that a photoelectric conversion unit itself formed on a semiconductor is symmetrical in regard to the boundary between the two pixel lines.
The above problem becomes more acute in case of a color image pickup apparatus. More specifically, an amplified solid-state image pickup apparatus often adopts a Bayer-arrangement color filter in which green pixels obliquely adjoin. In this case, a luminance signal of the sensor is controlled by a green-pixel signal. Here, even if the luminance of the light transmitted through a condensing lens is even throughout the pixel area as described above, a difference of the luminance signals at one-line intervals becomes large according to the pixel position closer to the end of the pixel area in the horizontal direction. As a result, image quality deteriorates.
Besides, in an image pickup apparatus which is applied to a color image pickup apparatus such as a three chips camera not adopting a color filter, a sensor signal is generally output by adding the signals of the above and below adjoining pixels through an interlacing operation. In such an example, both the centers of the openings of the above and below adjoining pixels are being shifted similarly in regard to the center of the pixel. For this reason, a difference of the added signals at one-line intervals becomes large according to the pixel position closer to the end of the pixel area in the horizontal direction. As a result, image quality deteriorates likewise.